As a method for winding a stator winding and/or a rotor winding of a rotary electrical machine including, for example, a motor, wave winding where a coil conductor is wound in a wavy state is known. As an example of a known rotary electrical machine having a wave winding configuration, a rotary electrical machine provided with a wave winding coil is disclosed in JP3952346B (hereinafter referred to as Patent reference 1). According to Patent reference 1, a three-phase wave winding configuration is established by using six pieces of coil sides that are arranged apart from each other by one slot pitch.
The coil side for one phase includes an up conductor portion at which a coil is wound in a direction away from a phase terminal and a down conductor portion at which the coil is wound in a direction closer to the phase terminal. The coil sides each wound in the wave winding are connected to each other in series at a side opposite to the phase terminal. Here, the winding wire that is serially connected in a manner that the up conductor portion includes the wave winding configuration is referred to as an up winding portion and the winding wire that is serially connected in a manner that the down conductor portion includes the wave winding configuration is referred to as a down winding portion. At a phase unit coil, that is, a winding coil for one phase, the up winding portion and the down winding portion are serially connected to each other.
However, Patent reference 1 discloses a known wave winding configuration where the number of kinds of the coil side at each magnetic pole of each phase is one, or a wave winding configuration including a stator structure in which the number of slots at each magnetic pole of each phase is one and which includes one kind of coil side that is accommodated in the slot of the stator. Here, in a case where there are plural kinds of the coil side at each magnetic pole of each phase or in a case where the stator structure includes plural number of the slots at each magnetic pole of each phase and thus the number of the kinds of the coil sides accommodated in the respective slots is increased to be plural, all the coil sides in the same phase need to be serially connected to each other because induced voltage generated at each coil side in the same phase differs from each other, and thus a circulating current in a phase is generated, which may lead to decrease in output of the rotary electrical machine. The known wave winding configuration will be described with reference to FIGS. 12 and 13.
FIG. 12 schematically illustrates a phase configuration of the rotary electrical machine including two kinds of coil side at each magnetic pole of each phase. The rotary electrical machine illustrated in FIG. 12 includes a known wave winding configuration where the number of kinds of the coil side at each magnetic pole of each phase is two or a wave winding configuration including a stator structure where the number of slots at each magnetic pole of each phase is two and including the two kinds of coil side accommodated in the slots of the stator. FIG. 13 schematically illustrates a connection status of U-phase coils illustrated in FIG. 12. FIG. 12 illustrates an example where the number of the kinds of the coil side at each magnetic pole of each phase is increased to be plural by connecting a phase unit coil 9X1 and a phase unit coil 9X2 (X refers to any one of phases U, V and W) with each other in parallel. For example, at a phase unit coil 9U1 of a U-phase, an up winding portion 9U1a and a down winding portion 9U1b are connected to each other in series, and at a phase unit coil 9U2, an up winding portion 9U2a and a down winding portion 9U2b are connected to each other in series. The same will apply to a V phase and to a W phase. The two kinds of the coil side at each magnetic pole of each phase are apart from each other by one winding pitch in a moving direction of a magnetic pole of a movable element.
Related to the two kinds of the coil side at each magnetic pole of each phase, the induced voltage generated at the phase unit coil 9U1 at which the coil sides of the same kind are serially connected to each other and the induced voltage generated at the phase unit coil 9U2 at which the coil sides of the same kind are serially connected to each other are different from each other. This is because the phase unit coil 9U1 and the phase unit coil 9U2 are in a same phase to each other (that is, the U phase), however, precisely speaking, phases thereof are different from each other as the coil sides thereof are apart from each other by one winding pitch in the moving direction of the magnetic pole of the movable element. For example, the induced voltage generated at the coil sides of the phase unit coil 9U1 is assumed to be higher than the induced voltage generated at the coil sides of the phase unit coil 9U2 at a predetermined time. In this case, the coil sides at which the respective induced voltages are relatively high are serially connected to each other at the phase unit coil 9U1, and the coil sides at which the respective induced voltages are relatively low are serially connected to each other at the phase unit coil 9U2. Where the induced voltages generated at the phase unit coils 9U1 and 9U2 are 9E1 and 9E2, respectively, the induced voltage 9E1 is higher than the induced voltage 9E2, and thus the circulating current is generated in the U phase. The above-mentioned explanation applies also to the V phase and the W phase, and output of the known rotary electrical machine is decreased due to the circulating current in each of the phases.
A need thus exists for a wave winding coil for a rotary electrical machine, which is not susceptible to the drawback mentioned above.